This invention claims priority of the German application 200 19 107.1 filed Nov. 12, 2000 which is incorporated by reference herein.
The invention relates to a stand, in particular for surgical microscopes, of the type having a pivotable support arm (2) to accommodate a load (G) and having a balancing force (FA) which acts on the support arm (2) via a working cable pull (24).
Surgical microscopes must be capable of being pivoted easily over a predefined range and should maintain a set position. For this reason, in the case of known stands, balance weights or compensation springs are provided, which compensate for the weight of the microscope and its additional devices. The balance weights are most frequently arranged in the manner of beam-type balances.
Particular embodiments of such beam-type balance arrangements are, for example, the xe2x80x9cOHS((trademark))xe2x80x9d design of the applicant, in which balance weights are displaced by parallelogram carriers from the top to the lower region of the stand, so that the overall centre of gravity of the stand is situated in the lower third of the stand structure. The basic construction of the OHS((trademark)) is illustrated symbolically in the international patent application WO 97/13997 of the applicant. In the case of this construction, rods form the connection between the support arm and balance weight.
The invention is concerned in particular with the question of increased operational safety in stands. The following statements from the prior art show that, hitherto there are still no optimum safety precautions in the event of material fractures for cable-assisted but also for other microscope stands.
In DE 197 42 050 A1, reference is made to an article xe2x80x9cGewichtsausgleich an feinmechanischen Gerxc3xa4ten [Weight compensation in precision mechanical devices]xe2x80x9d by H. Hilpert in Volume 2/1965 of the publication Feingerxc3xa4tetechnik [Precision Engineering], Volume 14.
In this article from the year 1965, various weight-compensating measures in precision engineering are discussed, being achieved primarily not by means of a counterweight but by means of spring-compensating measures (such as, by way of comparison, also in the scissors-arm construction of the MS 1 design from the applicant). In this case, safety aspects do not play any part.
DD 221571 A1 (1985) shows a stand design having a lever arm, at whose distal end there is a surgical microscope. The weight of the microscope is compensated for by a spring, which is connected to the lever arm via a cable pull. The basic adjustment of this surgical microscope is carried out by means of a threaded spindle, with which the end of the spring on the housing side is pulled further away from the lever arm or led closer to it. Changes in weight at the microscope are compensated for by the fact that the pivoting point of the cable pull is likewise adjusted relative to the lever arm via a spindle.
In order to achieve a uniform countermoment in all possible angular positions, it is necessary for the abovementioned point of action of the cable pull to be located on a connecting line between the axis of rotation of the lever arm and the mass centre of gravity of the microscope. This is achieved by operating an adjusting device in the form of a worm, which rotates a disc connected to the lever arm about the axis of rotation of the lever arm.
DE 3739080 A1 (1989) likewise specifies a spring device for balancing the weight for stands, in which cable pulls combined with springs are intended to lead to balancing. However, this concerns using force to support an adjusting movement which is exerted by an operator on a handle and not holding a load in a xe2x80x9cfloating statexe2x80x9d, as is desired in surgical microscopes. In the case of breakage of the spring or of the cable, the weight compensation disappears, and the load can fall suddenly.
By contrast, U.S. Pat. No. 5,397,323 (1992) presents a surgical robot with parallelogram carriers, in which, inter alia, the weight of the instrument is held in a weight-compensated fashion via a cable pull with the aid of a counterweight. The cable pull is of closed design in this case, that is to say one cable in each case is guided from the instrument up to the counterweight over an upper and lower deflecting roller (FIG. 3 of U.S. Pat. No. 5,397,323).
DE 19742050 A1 (1999) discloses a stand design having a pivotable parallelogram carrier which is weight-compensated via a cable pull and a balancing spring such that the balance weights which are additionally present and which act in accordance with the abovementioned principle of the balance can be designed to be particularly small. In this design, the cable pull is guided in a special way in order to minimize the balancing error, caused by the finite deflecting radius, in a wide pivoting range of the pivoting arm. The balancing error is, however, not eliminated by this measure, and so in specific pivoting positions it remains necessary to adjust the balance weights.
U.S. Pat. No. 6,070,839 (2000) discloses a further design having a pivoting arm and a cable pull-spring construction which permits pure balancing. In the case of changes in the weight, the pivoting point of the cable pull is displaced, in a fashion comparable to the design in the abovementioned DD 221571, over a spindle. A material fracture which may occur is not treated in this document.
U.S. Pat. No. 5,253,832 (1999) describes a stand having a cable pull and a centrally arranged tension spring for the balancing. This design offers no simple adjustability for changed loads. The cable accepts all of the load of the carrying arm and of the microscope.
In a design according to EP-A-866269, in order to transmit balancing weights, use is made of a toothed belt which can be kept braked by means of a brake. If a breakage occurs in the toothed belt, this can lead to the microscope falling onto the patient lying underneath it on the operating table.
All of the stand designs known hitherto and specified above, having cable pulls or toothed belts, have the same problems: in the event of breakage of the cable or of a tension spring, there is considerable disruption to the functioning of the instrument, which as a rule can lead to the sudden lowering of the load, and in the case of a surgical microscope to rapid, impermissible lowering of the microscope.
In particular during an operation, such a breakage could have catastrophic consequences for the patient. The obvious solution would be to dimension the cable used to be correspondingly thick, so that a breakage is virtually impossible. However, as the material thickness increases, the cable pulls become less mobile.
In questioning the dimensioning, it is also necessary to take account of the fact that, in extreme situations, the load or the weight on the load action point can rise in an extremely high manner. This is the case, for example, when a surgeonxe2x80x94for example perhaps because of nauseaxe2x80x94supports himself briefly on the microscope.
The invention is, then, based on the object of finding a safety mechanism which, in the event of a cable breakage, does not lead to the load being lowered. The invention is in this case not to be restricted merely to the use in a stand for surgical microscopes, but instead to any desired forms of stand in which force and/or balance compensation is performed by means of cable pulls.
This object is achieved by the provision of at least a second cable, the second cable being designed to be equivalent to the first cable and, in parallel, exerting the same functions as long as the first cable is intact. In the safety case (that is to say breakage of one of the two cables), it performs the working cable function on its own.
Alternatively, at least a second cable is placed to the side of the at least one working cable as a safety cable, being untensioned in the operating state and performing the functions of the working cable only in the safety state. According to the invention, this leads to the working resistance being substantially no higher than in the case of designs with only one cable, in spite of the use of two cable pulls, since the safety cable runs along virtually without friction and therefore without resistance.
In the sense of the invention, the term xe2x80x9ccablexe2x80x9d comprises all those design elements which are of cable-like, belt-like or chain-like design and serve to transmit load.
In the event of breakage of the working cable there is therefore only a minimum movement of the load (until the safety cable is tensioned), which therefore as a rule does not constitute any hazard. In the case of equivalent working cables without an actual safety cable, adaptation in the safety case is, if appropriate, likewise carried out via a rocker-like componentxe2x80x94preferably with limitation of the travel in order to limit the rocker movement.
According to a special refinement of the invention, a further safety mechanism is provided which is intended to prevent the stand continuing to be used over an unrestricted time period, although a working cable has been broken. Without this further safety mechanism, the operator would notice virtually no difference between working with the working cable and working with the safety cable. In the case of the broken working cable, according to the fundamental design of the invention, the device runs unchanged as before with the intact working cable, but with a loose safety cable. The further safety device provides that, as soon as the safety cable is active, a brake automatically comes into function which considerably increases the working resistance at the instrument, that is to say the resistance detected by the user when pivoting the load.
This high working resistance is intended to indicate to the user that the instrument must be subjected urgently to a service. In the course of the service, the broken working cable can then be replaced and the original state reproduced. However, the working resistance is not so high that an operation has to be interrupted or aborted because of the non-operability of the stand.
In a special refinement of the invention, the second safety mechanism is activated automatically, by the safety cable, which is originally not loaded, being loaded in tension. As soon as it is loaded in tension, the safety cable is forced into a wedge-like groove in a deflecting roller, in which it is subjected to a high frictional resistance. This is as distinct from a conventional throat-like running groove for the working cable, which opposes as little frictional resistance as possible to the cable run. The wedge-like groove can be protected, by means of a protective film made of plastic, metal or the like, against the cable inadvertently biting into the wedge groove, the said protective film only breaking and opening the path to eat into the wedge groove when a tensile force of a specific magnitude is exerted on the safety cable.
An alternative variant to the aforementioned design with an additional safeguard is a clamping element, which is arranged in a relative position in relation to the safety cable such that, in the unloaded state, the said safety cable passes loosely through the clamping element while, in the loaded state (in the tensioned state), it penetrates into the clamping element and is subjected there to increased friction.
The safety cable therefore interacts with a braking element whichxe2x80x94when the safety cable has taken over the pulling function in the event of breakage of the working cablexe2x80x94brakes the safety cable or a component connected to it, so that only emergency operation of the stand is still possible. The braking element can be a dedicated cable pinch brake (such as, for example, in the case of a sailing ship) but can also be a ratchet brake (as in an automatic safety belt) or a running roller with a particularly deep V groove or the like.
This design can be improved still further by a development by the safety cable being kept pressed in the loose direction by a tensioner, the tensioner being spring-loaded with a relatively low spring force which, in the event of cable breakage of the working cable, can easily be overcome by the tension in the safety cable.
The present invention will preferably be used in the case of a stand design according to the commonly owned patent applications DE 200 19 109, DE 200 19 105 and DE 200 19 106 (respectively corresponding to U.S. patent applications Ser. Nos. 10/010,103, 10/010,101, and 10/008,285) filed on the same date. However, it is not restricted to such designs. For the purpose of the possible later combination of at least two of the three patent applications, the disclosures in the above-listed applications are incorporated by reference into the disclosure of the present patent application.
Supports in the sense of the patent claims are to be understood both as individual support arms and also parallelogram carriers or similar constructions.